1. Field of the Invention
The present invention relates to a resonance ionization image detector system incorporating single photo-electron and photon detection principles, and a method for detecting and/or imaging using such system.
2. Discussion of the Related Art
The present invention provides a spectrally selective imaging optical detection system based on resonance ionization in an atomic vapor. The system provides improved spatial, spectral and temporal resolution compared with currently available techniques. The system finds application in the imaging of ultrasonic fields, high energy particle detection and optical communications.
The current trend in imaging science, i.e., spectrally resolved imaging detectors and filters, continues to attract the increasing attention of researchers from many different fields of applied optics and spectroscopy [Schaeberle et al, Anal. Chem., Vol. 67, "Raman chemical imaging: noninvasive visualization of polymer blend architecture," pages 4316-4321 (1995); Malonek et al, Science, Vol. 272, "Interaction between electrical activity and cortical microcirculation revealed by imaging spectroscopy: implication for functional brain mapping," pages 551-554 (1996); and Morris et al, Appl. Spectrosc., Vol. 50, "Liquid Crystal Tunable Filter Raman Imaging," pages 805-811 (1996)]. Imaging with even higher spectral resolution, limited only by the natural atomic linewidth, can be achieved using atomic resonance imaging spectrometers and filters. As a result, atomic imaging detectors have a very limited spectral range corresponding to the absorption frequencies of a few easily volatile elements. Nevertheless, as will be demonstrated herein, even with such a limited spectral range, atomic resonance imaging detectors and filters can have a surprisingly broad range of useful applications.
A limited number of concepts and applications for imaging atomic filters and detectors have been described in the literature. Ultra narrowband atomic resonance ionization image detectors were first suggested for the detection of single atoms and molecules in the presence of strong background radiation [Matveev, J. Appl. Spectrosc. (Russian), Vol. 46, "Atomic resonance spectrometers and filters," pages 359-375 (1987)]. An imaging atomic resonance monochromator with atomic Cs vapor [Korevaar et al, Proc. SPIE, Vol. 1059, "Imaging atomic line filter for satellite tracking," pages 111-118 (1989)] has been suggested and experimentally verified for space communication satellite tracking. A promising and interesting application for atomic and molecular filters is the detection of images of aerodynamic flow fields [Forkey et al, AIAA Journal, Vol. 34, "Demonstration and characterization of filtered Rayleigh scattering for planar velocity measurement," pages 442-448 (1996); Smith et al, AIAA Journal, Vol. 34, "Application of absorption filter planar Doppler velocimetry to sonic and supersonic jets," pages 434-441 (1996); McKenzie, AIAA Paper 95-0297, "Measurement capabilities of planar Doppler velocimetry," pages 1-5 (January 1995); Finkelstein et al, AIAA Paper 96-2269, "A narrow passband, imaging, refluorescence filter for non-intrusive flow diagnostics," pages 1-5 (1996); and Finkelstein et al, AIAA Paper 96-0177, "Cavity locked, injection seeded, titanium: sapphire laser and application to ultra violet flow diagnostics," pages 1-9 (1996)]. Prospects for applications of atomic and molecular Faraday filters for imaging purposes appear to be very promising. Presently, non-imaging variations of the Faraday atomic filter have found many useful applications for free-space and underwater communications systems, atmospheric temperature measurements and laser lidar [Chen et al, Optics Letters, Vol. 18, "Sodium-vapor dispersive Faraday filter," pages 1019-1021 (1993); Yin et al, Proc. SPIE, Vol. 2123, "Stark anomalous dispersion optical filter for doubled Nd: YLF lasers," pages 455-457 (1994); Chen et al, Proc. SPIE, Vol. 2123, "High-sensitivity direct detection optical communication system that operates in sunlight," pages 448-454 (1994); Hemmati, Proc. SPIE, Vol. 2629, "Laser communication component technologies: database, status and trends," pages 310-314 (1996); and Chen et al, Optics Letters, Vol. 21, "Daytime mesopause temperature measurement with a sodium-vapor dispersive Faraday filter in a lidar receiver," pages 1093-1095 (1996)]. Other promising applications for atomic high spectral resolution image detectors can be found, for example, in the detection of images of Raman and Rayleigh spectra of scattered radiation from micro and macro objects [Shimizu et al, Appl. Opt., Vol. 22, "High spectral resolution lidar system with atomic blocking filters for measuring atmospheric parameters," pages 1373-1381 (1983); and Smith et al, Optics Letters, Vol. 15, "Experimental demonstration of a Raman scattering detector based on laser-enhanced ionization," pages 823-825 (1990)].
In order to compare the relative merits of the different types of narrowband image detectors for the solution of a wide variety of practical problems, several characteristics must be specified:
(1) quantum efficiency--q (dimensionless) PA1 (2) intrinsic noise of the one-bit spatial element (pixel) of the image detector--N (usually electron/sec or electron/pulse) PA1 (3) active working area--A (cm.sup.2) PA1 (4) optical acceptance angle aperture--.DELTA..OMEGA.(sr) PA1 (5) spatial resolution--.DELTA.x (mm) PA1 (6) spectral bandwidth--.DELTA..lambda. (nm) or .DELTA..nu. (MHz or GHz) PA1 (7) spectral working range--S (GHz) PA1 (8) instrument function--I(.lambda.) PA1 (9) temporal resolution--.DELTA..tau. PA1 (1) detection of moving objects by Doppler shift of scattered radiation, e.g., aerodynamic or hydrodynamic flow, nuclear fusion, low temperature plasmas, products of combustion and explosions, wind flow, moving missiles, aircraft, automobiles, tanks, projectiles and even people; PA1 (2) vibration and oscillation characteristics, such as in the aerospace and automobile industries, and in measurement of oscillations in the Earth's crust; PA1 (3) detection and imaging of ultrasonic fields; PA1 (4) detection of single atoms or molecules in the atmosphere, flames, plasmas and other environments; PA1 (5) detection of high energy ionizing particle tracks (x-rays, .gamma.-rays, high energy electrons, protons, neutrons and elementary particles) using liquid or gas targets; PA1 (6) optical communications systems where high spectral and temporal resolution are needed; PA1 (7) deep UV microscopy (50-59 nm) for direct, non-scanning imaging detection of 3-D images; PA1 (8) satellite tracking; PA1 (9) mapping and range imaging; and PA1 (10) detection of moving objects.
It is an important object of the present invention to provide a narrowband imaging detector and a method for narrowband imaging that produces superior results, as evaluated in accordance with the above factors, to imagers or detectors that are currently available.